Coverage improvement in wireless systems with fixed infrastructure based relays

ABSTRACT

Infrastructure relays are used to relay signals to multi-antenna receivers where the received signals are then processed using MIMO processing. The transmissions can use spatial multiplexing and/or space time block coding.

RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 12/119,817 filed May 13, 2008, which claims thebenefit of, and is a divisional application of U.S. Pat. No. 7,406,060issued on Jul. 29, 2008, which claims the benefit of U.S. ProvisionalPatent Application No. 60/696,996 filed Jul. 6, 2005, which are allhereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to wireless systems such as cellular systems thathave fixed infrastructure-based relays, and to methods of improving thecoverage in such systems.

BACKGROUND OF THE INVENTION

Relays have been used to expand the coverage of conventional cellularsystems. With such relays, a mobile station that is out of range of thebase station may still be able to communicate with a base station viaone of the relays. The relay has very little functionality, typicallyonly re-transmitting signals received from the mobile station or fromthe base station.

MIMO (multiple input multiple output) systems feature multiple antennasat the transmitter and/or receiver, and spatial processing at thereceiver to recover transmitted data. Examples of existing MIMOtechnologies include STBC (space-time block coding) and spatialmultiplexing (SM) approaches.

With STBC (space-time block coding), each antenna transmits a respectivestream, and there is some correlation between the streams, either due tocoding and modulation of input data prior to block coding, or in theblock coding structure per se. STBC schemes involve a little morecomplexity at the transmitter, but may allow simplified receivercomplexity. An example of an STBC scheme that relies on coding andmodulation prior to block coding is the so-called “BLAST” approach inwhich each transmit antenna is used to transmit a unique symbol stream,with coding and modulation being employed prior to block coding tointroduce correlation. An example of an STBC scheme that relies on theblock coding structure per se is STTD (space time transmit diversity)where each symbol appears on multiple antennas. A well-known STTD schemeis Alamouti code-based transmission.

With spatial multiplexing (SM), each antenna is used to transmit anindependent data stream. There is no correlation introduced by codingand modulation. SM approaches have reduced transmitter complexity, butinvolve higher receiver complexity. Well known SM schemes include theso-called V-BLAST (vertical BLAST) and D-BLAST (diagonal BLAST) whereindependent symbol streams are transmitted on each antenna. With SM,independent data streams are transmitted over different antennas, togenerate a multiplexing gain. When used with Maximum Likelihooddecoding, such a scheme is found to provide good performance.

While traditional STBC exploits both the multiplexing gain as well asdiversity gain, spatial multiplexing systems such as V-BLAST provideprimarily a multiplexing gain. While the diversity gains levels off withincreasing number of antennas, the spatial multiplexing gain increaseslinearly with the increase in number of antennas.

The benefit of MIMO is significant when the SINRs of the MIMO signalsare comparable thereby allowing a full-rank MIMO channel realization.This restricts the number of instances where cooperative MIMO can besuccessfully employed in systems featuring distributed users havingvarying SINR conditions.

In systems employing cooperative MIMO, multiple mobile stationscooperatively transmit the data of a single mobile station so as toappear as a MIMO transmission. For example, two mobile stations with oneantenna each can transmit one of the mobile stations data. A two antennabase station could then receive the two signals and process them usingMIMO techniques. This scheme has some disadvantages. For example, itrequires each mobile station's data to be exchanged between the twomobile stations to enable cooperative transmission. Furthermore, thetransmission is opportunistic since it is based on access bandwidth inthe peer mobile station over and above its own prioritizedtransmissions. The scheme adds complexity to the mobile station in thatit requires an additional transceiver chain to transmit and receive datafrom its peers. Cooperative MIMO has been shown to provide significantcapacity improvements in cellular systems. Since the exchange betweentwo mobile stations is an essential component of cooperative MIMO, themobile stations need to be conveniently located to exchange theinformation. Thus, the application of cooperative MIMO is limited tosuch scenarios.

Infrastructure based 2-hop relaying with the use of cellular spectrumfor the relaying function has also been shown to provide significantcoverage improvement in cellular systems, resulting in greater ubiquityof data rates as the user moves around the cell. Despite the fact thatthe bandwidth resource at the base station is now used for both themobile station-to-relay transmissions and relay-to-base stationtransmissions, the improved SINR conditions on each of the two hopsresult in a higher aggregate SINR on the link as a whole and thereforeimproves the coverage to mobile stations that are further away from thebase station.

FIG. 1 shows an example of conventional fixed infrastructure basedselective relaying. Shown is a base station 10 having nominal coveragearea 12. Fixed infrastructure relays 14,16 are also provided each withrespective coverage areas 18,20. It can be seen that the relays serve toincrease the coverage area of the base station. Mobile stations such asmobile station 22 that are within the coverage area 12 of the basestation 10 can communicate directly with the mobile stations such asmobile stations 24 and 26 that are outside the coverage area of the basestation 10, but that are within the coverage area of one of the relayssuch as relay 14, can communicate by first communicating to the relay 14and then having their signals relayed from the relay 14 to the basestation 10 as illustrated. The result is a multi-hop extension ofcellular communication. Various FDD (frequency division duplexing)/TDM(time division multiplexing) approaches have been proposed for dealingwith the transmission between the mobile stations and between relays andthe base station. In a particular example illustrated at 30, a cellularbase station 10, a relay 14 and a mobile station 24 communicate usingcombined FDD/TDD such that during a first time interval T₁ the basestation 10 and the relay 14 communicate using uplink and downlinkfrequencies f_(UL) and f_(DL) respectively while during a second timeperiod T₂ the mobile station 24 and the relay 14 communicate usinguplink and downlink frequencies f_(DL) and f_(UL).

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides a methodcomprising: a first wireless node transmitting to a second wirelessnode; a third wireless node transmitting to the second wireless node;the second wireless node performing MIMO processing on signals receivedfrom the first wireless node and the third wireless node; wherein atleast one of the first and third wireless nodes is re-transmittingcontent received from a fourth wireless node.

In some embodiments, the first wireless node is a mobile station; thesecond wireless node is a base station; the third wireless node is arelay; the fourth wireless node is a mobile station.

In some embodiments, the method further comprises: wherein the first andthird wireless nodes re-transmit signals received from fourth and fifthwireless nodes respectively.

In some embodiments, the first and third wireless nodes are relays; thesecond wireless node is a base station; the fourth and fifth wirelessnodes are mobile stations.

In some embodiments, the method further comprises: the first and thirdwireless nodes receiving signals from fourth and fifth wireless nodesrespectively; the first node transmitting content received from thefourth wireless node to the third wireless node, and the third wirelessnode transmitting content received from the fifth wireless node to thefirst wireless node; wherein first wireless node transmitting to thesecond wireless node comprises transmitting a signal based on thecontent received from the third wireless node and also based on thecontent received from the fourth wireless node; wherein the thirdwireless node transmitting to the second wireless node comprisestransmitting a signal based on the content received from the firstwireless node and also based on the content received from the fifthwireless node.

In some embodiments, the first and third nodes transmissions togethercomprise an STTD (space time transmit diversity) transmission.

In some embodiments, the method further comprises providing a furthermode of operation for the fourth node comprising: the fourth nodetransmitting directly to the second node and to the third node; thethird node receiving from the fourth node and re-transmitting to thesecond node, the third and fourth node's transmissions comprising acooperative diversity transmission; the second node receiving a directtransmission from the fourth node and the third node's retransmission onmultiple antennas and performing diversity combining; the method furthercomprising: adaptively selecting one of another MIMO mode andcooperative diversity.

In some embodiments, the method further comprises adaptively selectingone of a plurality of MIMO modes by: for each MIMO mode determining arespective metric; selecting between the plurality of MIMO modes basedon the metrics.

According to another broad aspect, the invention provides a methodcomprising: using STBC, transmitting content on N>=2 antennas;transmitting content on M>=1 additional antennas; performing spatialmultiplexing processing on signals received on at least N+M antennas toextract components relating to the content transmitted by the N antennasand components relating to the content transmitted by the M antennas;performing STBC processing on the components relating to the contenttransmitted by the N antennas to recover the content transmitted usingSTBC.

In some embodiments, the N antennas are on different wireless nodes.

In some embodiments, at least one of the antennas is on a relay relayingcontent received from another wireless node.

In some embodiments, the method further comprises: adaptively addingand/or removing antennas from the set of N+M antennas used to transmitthe content.

According to another broad aspect, the invention provides a systemcomprising: a MIMO processing node having at least two antennas; a firstrelay node; the MIMO processing node being adapted to perform MIMOprocessing on signals received from the first relay node and at leastone other node.

In some embodiments, the first relay node is relaying a signal receivedfrom other than one received directly from the at least one other node.

In some embodiments, the first relay node is relaying a signal receivedfrom the at least one other node.

In some embodiments, said at least one other node comprises a secondrelay node.

In some embodiments, the first and second relay nodes exchange first andsecond content received for relaying and transmit respective signalsbased on both the first and second content to the MIMO processing node,the respective signals collectively comprising an STBC signal.

According to another broad aspect, the invention provides the MIMOprocessing node comprising: at least N+M antennas adapted to receivesignals from transmissions comprising an STBC transmission from N>=2antennas and transmissions on M>=1 additional antenna; a spatialmultiplexing processor for performing spatial multiplexing processing onsignals received on at least N+M antennas to extract components relatingto the content transmitted by the N antennas and components relating tothe content transmitted by the M antennas; an STBC processor forperforming processing on the components relating to the contenttransmitted by the N antennas to recover the content transmitted usingSTBC.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the attached drawings in which:

FIGS. 1A and 1B show conventional infrastructure based relaytransmission;

FIG. 2A is a network diagram showing an example of cooperative MIMOusing infrastructure based relays as provided by an embodiment of theinvention;

FIG. 2B is a flowchart of an example method of cooperative MIMO providedby an embodiment of the invention;

FIGS. 3A and 3B are schematics of example networks showing cooperativeMIMO using infrastructure based relays as provided by an embodiment ofthe invention;

FIG. 3C is a flowchart of an example method of cooperative MIMO providedby an embodiment of the invention;

FIGS. 4A through 4C are network diagrams of further examples employingcooperative MIMO with infrastructure based relays provided by anembodiment of the invention;

FIGS. 4D and 4E are flowcharts of two further example methods ofcooperative MIMO provided by an embodiment of the invention;

FIG. 5A is a schematic of an example network showing cooperativediversity provided by an embodiment of the invention;

FIG. 5B is a flowchart of an example method of performing cooperativediversity provided by an embodiment of the invention;

FIG. 6 is a schematic of an example network showing adaptation betweencooperative diversity and cooperative MIMO in accordance with anembodiment of the invention;

FIG. 7 is a flowchart of an example method of performing adaptationbetween cooperative MIMO and cooperative diversity provided by anembodiment of the invention;

FIG. 8 is a schematic of an example network showing sequential MIMOprocessing using multiple MIMO nodes;

FIG. 9 is a flowchart of another MIMO method provided by an embodimentof the invention;

FIG. 10 is a flowchart of another MIMO method provided by an embodimentof the invention; and

FIG. 11 is a block diagram of an example MIMO processing node providedby an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 2A, a first example of a MIMO system employingfixed infrastructure based selective relaying will be described. Shownis a fixed infrastructure consisting of a base station 80 having twoantennas 82,84 and a relay 86 having two antennas 88,90. Antenna 88 isdirected towards the base station 80 whereas antenna 90 is pointed awayfrom the base station to provide additional coverage, either in terms ofdata rate ubiquity and/or physical coverage area.

In operation, mobile stations that are within the direct coverage areaof the base station 80 communicate directly with the base station. Anexample of this is mobile station 92 whose transmissions 96 are showngoing directly from the mobile station 92 to the base station 80. Mobilestations that are within the coverage area of the relay 86 firsttransmit to the relay 86 and then the relay 86 forwards theircommunications on to the base station 80. For example, mobile station 94is shown transmitting a signal 98 that is received by the relay 86 onantenna 90. This is then re-transmitted via antenna 88 as signal 100towards the base station 80.

The base station 80 then processes the signals received on its twoantennas 82,84 using MIMO processing techniques. In the particularexample illustrated, what is formed is a virtual 2:2 MIMO spatialmultiplexing system using, e.g., V-BLAST mode. In other words, this isanalogous to a two antenna transmitter transmitting unique data on eachtransmitter. Each antenna of the two antenna receiver receives a signalcontaining transmissions from both transmit antennas. Preferably, whensuch a MIMO transmission is set up the transmissions are synchronized bybase station scheduling. In the illustrated example, this would involvesynchronizing the transmissions of the mobile station 92 and the relay86. Unlike conventional co-operative MIMO, for the embodiment of FIG. 2Athere need not be any direct cooperation between mobile station 92 andrelay 86.

The base station 80 performs MIMO processing by processing the signalsreceived on antennas 82 and 84 together so as to extract the signals 96and 100 sent from mobile station 92 and relay 86, respectively. Theideal detection technique for spatial multiplexing is very complex,based on Maximum likelihood decoding. Other suboptimal techniques arealso available. However, since the base station processes the receivedsignal, receiver complexity is not an issue. Techniques for performingsuch MIMO processing are well known in the art and will not be describedin further detail here. See for example P. W. Wolniansky, G. J.Foschini, G. D. Golden, R. A. Valenzuela, V-BLAST: An Architecture forRealizing Very High Data Rates Over the Rich-Scattering WirelessChannel, in Proc. ISSSE-98, Pisa, Italy, Sep. 29, 1998.

While the example presented here addresses 2×2 MIMO, the concept may beextended to a larger number (N) of relays and mobile stations to formN×M MIMO channel at the receiver. Since there is no exchange of databetween the two transmitting (mobile, relay) stations, there is norequirement for the two stations to be conveniently located within reachof each other.

Referring now to FIGS. 3A and 3B, a second example of a MIMO systememploying fixed infrastructure based selective relaying will now bedescribed. In both FIGS. 3A and 3B, there is fixed infrastructureconsisting of a base station 110 having two antennas 112,114, and a pairof relays 116,122. Relay 116 has two antennas 118,120, and relay 122 hastwo antennas 124,126. FIG. 3A shows the transmissions 134,136 of a pairof mobile stations 130,132. In the illustrated example, mobile station130 is within the coverage area of relay 116 whereas mobile station 132is within the coverage area of relay 122.

The transmissions by the relays 116,122 are shown in FIG. 3B. Relay 116forwards on the signal received from the mobile station 130 as indicatedat 140, and relay 122 forwards on the signal received from mobilestation 132 as indicated at 142. The base station 110 receives the twosignals on its two antennas 112,114 and the base station performs MIMOprocessing to recover the transmissions of each of the mobile stations130,132. Preferably, the transmissions of the relays 116,122 aresynchronized, for example using base station scheduling. In the exampleof FIGS. 3A and 3B, the net effect is a virtual 2:2 MIMO system withV-BLAST mode. Again, any number of relays may participate to form an N×Mspatial multiplexing channel where M is the number of Base stationantennas. Also, there is no requirement for the relays to have goodcommunication channels between them to exchange data.

Referring now to FIGS. 4A and 4B, shown is another example of a MIMOsystem employing fixed infrastructure based selective relaying, wherethe relays have a communications channel between them. For example, theymight be in proximity to each other, such that they can form atransmission channel between themselves for cooperation. In both FIGS.4A and 4B, fixed infrastructure is shown consisting of a base station160 having antennas 162,164, and a pair of relays 166,172. Relay 166 hasantennas 168,170 and relay 172 has antennas 174,176. Transmissions of apair of mobile stations 180,182 and between the relays 166,172 areindicated in FIG. 4A. This starts with the mobile station 180 making itstransmission 184 that is received by relay 166, and mobile station 182making its transmission 186 that is received by relay 172. The tworelays 166,172 which have a transmission channel between themselves thenexchange the information that they receive from the respective mobilestations 180,182. This exchange of information is indicated at 188. Atthis point, both relays 166,172 have knowledge of the signals receivedfrom both mobile stations 180,182. Coding and/or modulation is performedto combine the data/signals.

Using this information, various STBC MIMO transmissions can be made. Afirst example is indicated in FIG. 4B. In this example, the first relay166 transmits f₁ (a,b) where “a” is the first mobile station's contentand “b” is the second mobile station's content. The relay 172 transmitsf₂ (a,b). The result is virtual 2:2 MIMO, e.g., with BLAST mode.

In another STBC MIMO example, the signals received from the two mobilestations 182,184 are combined using STTD (space-time transmitdiversity), e.g., Alamouti coding. For example, if “a” is the signalfrom mobile station 180 and “b” is signal from mobile station 182, thenthe transmissions from the two relays 166,172 can be constructed as thefirst relay 166 transmitting “a” during time interval T₁ andtransmitting “b” during time interval T₂ and the second relay 172transmitting “−b*” during time interval T₁ and “a*” during time intervalT₂.

In this example, the first relay transmits {a, b} in sequence over twotime intervals T₁, T₂ and the second relay transmits {−b*, a*} over thesame two time intervals, wherein b* and a* are the complex conjugates ofb and a, respectively. The base station then performs MIMO processing torecover a and b. This is shown in FIG. 4C. This figure is identical toFIG. 4B except now the first relay 166 is shown transmitting signal 190consisting of {a, b} in sequence, and the second relay 172 is showntransmitting signal 192 consisting of {−b*, a*} in sequence.

Both techniques illustrated in FIG. 3 (spatial multiplexing) and FIG. 4(STBC) may be used with different sets of relays, with the base stationadapting the receiver algorithm according to whether spatialmultiplexing or STBC has been used. Since the relays are staticentities, the base station will have the knowledge as to which sets ofrelays can use STBC and which others can use spatial multiplexing.

Referring now to FIG. 5A, shown is yet another example of a MIMO systememploying fixed infrastructure based selective relaying. This exampleincludes fixed infrastructure consisting of a base station 50 havingantennas 52,54 and a relay 56 having antennas 58,60. With this example,a single mobile station 70 is illustrated transmitting its signal 72.The signal is received by the relay 56 and re-transmitted at 74. Thebase station 50 receives the signal 72 directly from the mobile station70 and receives the signal 74 from the relay. The transmission that isdirectly received will be received earlier by the base station 50 andthe base station will store soft information determined for thisreception. After receiving the newer transmission 74, the base station50 processes the new relay transmission together with the direct mobilestation transmission 72.

Thus, at a first instant, receive antenna diversity takes place at thebase station 50 to receive a copy of the mobile station's directtransmission at time T₁ on receive antennas 52,54. Shortly later,antenna diversity is used at the base station to receive two copies ofthe signal transmitted by the relay 56 at time T₂ on receive antennas52,54. These signals are all then combined to recover the originaltransmission. This can be considered a “cooperative diversity” approachin that the same two antennas are used to provide antenna diversity fromthe mobile station 70 and from the relay 58, but at different times.

The transmissions 72 and 74 may occur within the same receive processinginterval (with some delay on path 74), for example if the relay is ananalog relay. In this case, the signal may be processed at the receiveras a 2×2 MIMO signal. Alternatively, the transmissions from 72 and 74may occur far enough apart to be received during different receiveprocessing intervals. In this case, soft samples from the two timeintervals may be processed collectively by soft combining.

Scheduling

The base station is responsible for scheduling transmissions from themobile stations as well as from the relays to the base station. The basestation scheduler treats the relays as terminals for the purpose ofscheduling.

Preferably, for MIMO transmissions, the base station schedules the MIMOtransmissions in a deterministic manner, based on the schedulingpriorities of the different mobile stations.

For the embodiment of FIG. 2A, the following scheduling decisions can bemade to synchronize transmissions:

-   -   Mobile station 94 to Relay 86: T1    -   Mobile station 92 to base station 80 and Relay 86 to base        station 80: T2

For the embodiment of FIG. 3A, the following scheduling decisions can bemade in order to synchronize transmissions:

-   -   Mobile station 130 to Relay 116, mobile station 132 to Relay        122: T1    -   Relay 116 to base station 110 and Relay 122 to base station 110:        T2

For the embodiment of FIG. 4A, the following scheduling decisions can bemade to synchronize transmissions:

-   -   Mobile station 180 to Relay 166 and mobile station 182 to Relay        172: T1    -   Exchange between Relays 166,172: T2    -   Relay 166 to base station 160 and Relay 172 to base station 160:        T3

For the embodiment of FIG. 5A, the following scheduling decisions can bemade to synchronize transmissions:

-   -   Mobile station 70 to Relay 56 and base station 50: T1    -   Relay 56 to base station 50: T2

Various examples of MIMO and cooperative diversity have been described.In another embodiment, an adaptation between cooperative diversity andanother MIMO scheme is performed. This involves on a per mobile stationand/or relay pair basis comparing MIMO processing gains with diversitygains. An appropriate selection of the better performance can then bemade. Adaptation may also be used to switch between any of the MIMOmodes described herein, including STBC, SM and cooperative diversity.The particular modes to be adapted between can be selected on animplementation specific basis. The frequency of making this selectionmight for example depend on the channel update rate.

Preferably, the relays operate on the cellular channel in a TDM fashion,meaning that they do not receive and transmit at the same time. However,other approaches may be employed that allow the relays to transmit andreceive at the same time, for example using co-channel separation orfrequency division duplexing, or analog relaying.

An example of adapting between two MIMO modes is shown in FIG. 6. Inthis example, there is a base station 200 with antennas 202,204. Alsoshown is a pair of relays 206,208 each of which has a pair of antennasas in previous embodiments. The transmissions during the firstadaptation period AP₁ from the relays 206,208 and a pair of mobilestations 212,214 are indicated at 216. In this case, MIMO is beingemployed with each mobile station's signals being transmitted viarespective relays to the base station 200 where MIMO processing isperformed. At a later adaptation period AP₂, the signals that aretransmitted are indicated at 218. In this case, the second mobilestation 214 has a signal that is transmitted via the relay 208, and thesignal is also directly received at the base station 204. As such, acooperative diversity mode is being implemented at AP₂. Adaptation canbe performed to optimize overall system performance.

Referring now to FIG. 7, shown is a flowchart of an example method ofadaptive selection between two MIMO modes. At step 7-1, a determinationof a metric for a first MIMO mode is calculated. At step 7-2, a metricfor a second MIMO mode is calculated. At step 7-3, a selection is madebetween the first and second MIMO modes based on the two metrics. Themetrics can be computed in any appropriate place within the network. Themost convenient place to calculate them in a cellular environment wouldbe at the base station. More generally, this method can be used toselect between a plurality of MIMO modes.

All of the above embodiments have assumed that the base station has twoantennas and therefore allows for 2:2 STBC and/or 2:2 SMimplementations. More generally, any appropriate number of antennas canbe implemented at the base station, and any MIMO/cooperative diversityschemes supported by such antennas can be implemented. For example, N×MBLAST or N×M V-BLAST could be employed for an N antenna receiver and Mtransmit antennas where (N, M)>2.

While the embodiments described thus far have focussed on cellularsystems, it can be readily seen how these approaches can also be appliedto mesh networks. In a mesh network, the functionality of the abovedescribed BTS and relay or relay pairs would be implemented by two orthree nodes within the mesh network to provide cooperative MIMO and/orcooperative diversity schemes.

FIG. 2B is a flowchart of an example MIMO transmission method similar tothe method described with reference to FIG. 2A above, but applied in abroader context of four nodes. Any of these nodes may be mobilestations, relays or base stations or mesh networking nodes or othernodes for example. At step 2-1, a first node transmits to a second node.At step 2-2, the second node re-transmits to a third node. At step 2-3,a fourth node transmits to the third node. Finally, at step 2-4, thethird node performs MIMO processing of the signals received from thesecond and fourth nodes.

FIG. 3C is a flowchart of an example method similar to that describedabove with reference to FIGS. 3A and 3B, but applied in a broadercontext of five nodes. Any of these nodes may be mobile stations, relaysor base stations or mesh networking nodes or other nodes for example.The method begins at step 3-1 with a first node transmitting to a secondnode and a third node transmitting to a fourth node. At step 3-2, thesecond and fourth nodes re-transmit to the fifth node in sync. At step3-3, the fifth node performs MIMO processing.

Referring now to FIG. 4D shown is a flowchart of an example method ofMIMO transmission that is similar to that described above with referenceto FIGS. 4A, 4B and 4C, but applied in a broader context of five nodes.Any of these nodes may be mobile stations, relays or base stations ormesh networking nodes or other nodes for example. At step 4-1, a firstnode transmits to a second node, and a third node transmits to a fourthnode. At step 4-2, the second and fourth nodes exchange the first andthird node's signals. At step 4-3, the fourth node transmits a signalbased on both the first node's content and the third node's content, andthe second node transmits a signal based on the first node's content andthe third node's content. At step 4-4, the fifth node performs MIMOprocessing.

Referring now to FIG. 4E, shown is another method that is a particularexample of the method of FIG. 4D. Step 4-6 is implemented as aparticular example of step 4-3 of FIG. 4D. This consists of the secondand fourth nodes transmitting an STTD signal containing content of boththe first and third nodes.

Referring now to FIG. 5B, shown is a flowchart of a method ofcooperative diversity transmission similar to that described above withreference to FIG. 5A, but applied in a broader context of three nodes.Any of these nodes may be mobile stations, relays or base stations ormesh networking nodes or other nodes for example. At step 5-1, a firstnode transmits to a second node and a third node. A single signal istransmitted, but this is received by both the second and third nodes. Atstep 5-2, the second node receives the signal and re-transmits thesignal to the third node. At step 5-3, the third node receives thedirect transmission and then later receives the second node'sre-transmission on multiple antennas. The base station then performsMIMO processing on the signals received from the first node and thesecond node.

Note that in the above embodiments, the selection of which wirelessnodes are to participate in a given cooperative MIMO transmission orcooperative diversity transmission can be statically defined, ordynamically defined. For implementations where one or more of thewireless nodes are mobile stations, the nodes will need to bedynamically defined to accommodate the movement of the mobile node. Insuch a context, with reference to FIGS. 2A and 2B for example, assumingthat the “fourth wireless node” is the mobile station, then whatconstitutes the first, second and third wireless nodes from that mobilestation's perspective can change over time.

In embodiments featuring adaptive selection between cooperative MIMO,and cooperative diversity, the nodes involved in the two methods be thesame or may be different.

All of the embodiments have assumed 2×2 MIMO implementations. It isreadily apparent how these can be extended to handle MIMO transmissionshaving larger dimensions.

Referring now to FIG. 8, shown is a network diagram of an example MIMOsystem in which there is sequential MIMO processing using multiple MIMOmodes. Shown is a base station 200 having four antennas 201. Also shownare three relays 202,204,206. Mobile stations are indicated at208,210,211,212. At the particular instant depicted, mobile station 208is sending its transmissions to relay 202 and mobile station 210 issending its transmissions to relay 204. Relays 202 and 204 exchangecontent as indicated at 214 and generate an STBC signal 216 that istransmitted towards the base station 200. Any STBC format can beemployed. In effect, the two mobile stations 208,210 are having theirsignals transmitted in a manner analogous to that of FIG. 4 as discussedabove. At the same time, mobile station 211 is sending its signaldirectly to the base station 200, and mobile station 212 sending itssignal to the base station 200 via relay 206.

The base station 200 receives on its four antennas 201 and initiallyperforms spatial multiplexing processing. For example, it might performV-BLAST processing to resolve what was transmitted on each of the fourincoming signals. Having performed spatial multiplexing processing, thesignals received from the mobile station 211 and the mobile station 212via the relay 206 will be recovered directly. To recover thetransmissions of mobile stations 208,210, further MIMO processing mustbe performed to extract the respective signals from the STBC signaljointly transmitted by the two relays 202,204.

Thus, it can be seen that for the content ultimately originating frommobile stations 208,210, a sequential MIMO processing approach isemployed in the base station 200. First a spatial multiplexingprocessing is performed to extract streams relevant to the two mobilestations. Then a STBC processing is performed to extract mobile stationspecific streams. It is common to refer to different streams in spatialmultiplexing as “layers” and to the MIMO processing that is performed aslayer decomposition. In the above scenarios it is assumed that theoverall spatial multiplexing is equivalent to a V-BLAST transmission,but other spatial multiplexing approaches can alternatively beimplemented.

Referring now to FIG. 9, shown is a flowchart of a method performingMIMO transmission as provided by an embodiment of the invention. At step9-1, N≧2 nodes transmit using STBC. At the same time, at step 9-2 M≧1other nodes are transmitting. Note that the other nodes may also includecombinations of nodes that are transmitting STBC and/or nodes that aretransmitting using spatial multiplexing, or only a single other node. Atstep 9-3, performing spatial multiplexing processing to extractcomponents relating to content transmitted by the N antennas andcomponents relating to content transmitted by the M antennas using atleast N+M receive antennas. After this has been done, appropriatesubsets of the spatial multiplexing processed symbols are then furtherprocessed using STBC processing to recover the STBC content at step 9-4.

Applying numbers for the scenario of FIG. 8, there were N=2 nodes,namely relays 202,204, that were transmitting using STBC. There were M=2nodes, namely the mobile station 211 and the relay 206 that weretransmitting respective streams, effectively amounting to spatialmultiplexing. Then, the base station performed spatial multiplexingprocessing to extract the N+M=4 layers. The layers that were extractedin respect of signals received from the relays 202,204 were thenprocessed using STBC processing to recover that which was transmittedfrom each of the two mobile stations 208,210.

In an even further generalization, the method of FIG. 9 can be appliedin the context of multiple layers being transmitted by a single node.For example, in step 9-1, where there are N≧2 nodes transmitting STBC,more generally N≧2 transmit antennas can be transmitting STBC, theantennas being either on one or more different nodes. Similarly, in step9-2 M≧1 nodes are said to be transmitting, but more generally M≧1antennas are transmitting in addition to the antennas referred to instep 9-1 that are transmitting using STBC.

Referring now to FIG. 10, shown is a flowchart of an example method ofperforming MIMO transmission as provided by an embodiment of theinvention. At step 10-1, N≧2 antennas transmit using STBC. At the sametime, at step 10-2 M≧1 other antennas are transmitting. Note that theother antennas may also include combinations of antennas that aretransmitting STBC and/or antennas that are transmitting using spatialmultiplexing, or only a single other antennas. At step 10-3, performingspatial multiplexing components relating to content transmitted by the Nantennas and components relating to content transmitted by the Mantennas using at least N+M receive antennas. After this has been done,appropriate subsets of the spatial multiplexing processed symbols arethen further processed using STBC processing to recover the STBC contentat step 10-4.

Applying numbers for the scenario of FIG. 8, there were N=2 antennas,namely relays 202,204, that were transmitting using STBC. There were M=2antennas, namely the mobile station 210 and the relay 206 that weretransmitting respective streams, effectively amounting to spatialmultiplexing. Then, the base station performed spatial multiplexingprocessing to extract the N+M=4 layers. The layers that were extractedin respect of signals received from the relays 202,204 were thenprocessed using STBC processing to recover that which was transmittedfrom each of the two mobile stations 208,210.

In an even further generalization, the method of FIG. 10 can be appliedin the context of multiple layers being transmitted by a single node.For example, in step 10-1, where there are N≧2 antennas transmittingSTBC, more generally N≧2 transmit antennas can be transmitting STBC, theantennas being either on one or more different antennas. Similarly, instep 10-2 M≧1 antennas are said to be transmitting, but more generallyM≧1 antennas are transmitting in addition to the antennas referred to instep 10-1 that are transmitting using STBC.

Preferably, at least one of the nodes referred to above in FIG. 9 is arelay in which case the method becomes a special case of one or more ofthe previously discussed methods.

For the methods of FIGS. 9 and 10, it can be seen how this can begeneralized to accommodate multiple STBC groups that would be processedseparately after spatial multiplexing processing at the receiver. Forexample, two antenna STBC transmissions could be received by a fourantenna receiver where spatial multiplexing is performed first and thentwo separate STBC processings are performed.

Furthermore, antennas can be adaptively added and/or removed from agiven group of N+M transmit antennas, for example due to movement ofmobile nodes, addition of further mobile nodes in a coverage are. Inaddition, the manner in which the antennas are allocated for STBCtransmission can also be adaptively selected.

In a generalization that encompasses both the embodiments of FIGS. 2Aand 5A, a system is provided that has a MIMO processing node having atleast two antennas. This might be a base station or other wireless node.There is a first relay node (such as relay 86 of FIG. 2A or relay 56 ofFIG. 5A). The MIMO processing node performs MIMO processing on signalsreceived from the first relay node and at least one other node. In FIG.2A, the at least one other node is mobile station 92, and in FIG. 5A,the at least one other node is mobile station 70.

In some embodiments, the first relay node is relaying a signal receivedfrom other than one received directly from the at least one other node.This is the case for the example of FIG. 2A where the relay is relayingcontent received from mobile station 94. In other embodiments, the firstrelay node is relaying a signal received from the at least one othernode. This is the case for FIG. 5A where the relay 56 is relayingcontent received from mobile station 70 which is the “at least one othernode”.

In some embodiments, the first and second relay nodes exchange first andsecond content received for relaying and transmit respective signalsbased on both the first and second content to the MIMO processing node,the respective signals collectively comprising an STBC signal. The STBCsignal can be any of the types discussed herein, or some other STBCformat.

Another embodiment provides a MIMO processing node that functions as thereceiving node for any of the above-described methods. For example, aMIMO processing node suitable for implementing the receive aspects ofFIGS. 9 and 10 is depicted in FIG. 11 generally indicated at 300, andcan be a base station or some other wireless node. The MIMO processingnode 300 has at least N+M antennas 301 adapted to receive signals fromtransmissions comprising an STBC transmission from N>=2 antennas andtransmissions on M>=1 additional antenna. There is a spatialmultiplexing processor 302 for performing spatial multiplexingprocessing on signals received on at least N+M antennas to extractcomponents relating to the content transmitted by the N antennas andcomponents relating to the content transmitted by the M antennas. Thereis also an STBC processor 304 for performing processing on thecomponents relating to the content transmitted by the N antennas torecover the content transmitted using STBC. While shown as physicallydistinct entities, the SM processor 302 and the STBC processor 304 couldalternatively be combined. Any one or suitable combination of hardware,firmware and software can be used to implement the processors.

Some of the embodiments have been described as methods or systems inwhich multiple nodes are participating. Further embodiments of theinvention provide individual wireless nodes that are acting out theirroles in one or combination of methods or systems as described herein.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

We claim:
 1. A Multiple Input Multiple Output (MIMO) processing method,comprising: a first wireless node transmitting to a second wirelessnode; a third wireless node transmitting to the second wireless node;and the second wireless node performing MIMO processing on signalsreceived from the first wireless node and the third wireless node;wherein the third wireless node retransmits content received from afourth wireless node.
 2. The method of claim 1, wherein the firstwireless node is a mobile station.
 3. The method of claim 1, wherein thesecond wireless node is a base station.
 4. The method of claim 1,comprising the second wireless node adaptively selecting one of aplurality of MIMO modes by: for at least one MIMO mode determining atleast one metric; and selecting between the plurality of MIMO modesbased at least on the at least one metric.
 5. The method of claim 4,wherein the at least one metric comprises at least one of MIMOprocessing gains and diversity gains.
 6. The method of claim 4, whereinthe MIMO modes comprise at least one of Space Time Block Coding (STBC),Spatial Multiplexing (SM) and cooperative diversity.
 7. A Multiple InputMultiple Output (MIMO) processing method, comprising: a first wirelessnode transmitting to a second wireless node; a third wireless nodetransmitting to the second wireless node; and the second wireless nodeperforming MIMO processing on signals received from the first wirelessnode and the third wireless node; wherein the first and third wirelessnodes receive signals from fourth and fifth wireless nodes respectively.8. The method of claim 7, wherein: the first wireless node transmitscontent received from the fourth wireless node to the third wirelessnode; and the third wireless node transmits content received from thefifth wireless node to the first wireless node.
 9. The method of claim8, wherein: the first wireless node transmitting to the second wirelessnode comprises transmitting a signal based on both the content receivedfrom the third wireless node and the content received from the fourthwireless node; and the third wireless node transmitting to the secondwireless node comprises transmitting a signal based on both the contentreceived from the first wireless node and the content received from thefifth wireless node.
 10. The method of claim 7, wherein the firstwireless node transmitting to the second wireless node is synchronizedwith the third wireless node transmitting to the second wireless node.11. The method of claim 10, wherein the first wireless node transmittingto the second wireless node is synchronized with the third wireless nodetransmitting to the second wireless node by scheduling the firstwireless node transmitting to the second wireless node and schedulingthe third wireless node transmitting to the second wireless node. 12.The method of claim 11, wherein the scheduling is performed by thesecond wireless node.
 13. A Multiple Input Multiple Output (MIMO)processing method, comprising: selecting a group of N+M antennas tocooperate in a MIMO transmission, N being at least 2 and M being atleast 1; using Space Time Block Coding (STBC), transmitting content onthe N antennas; transmitting content on the M antennas; performingspatial multiplexing on signals received on at least N+M antennas toextract components relating to the content transmitted by the N antennasand components relating to the content transmitted by the M antennas;performing STBC processing on the components relating to the contenttransmitted by the N antennas to recover the content transmitted by theM antennas.
 14. The method of claim 13, wherein selecting a group of N+Mantennas to cooperate in a MIMO transmission comprises staticallydefining the group of N+M antennas.
 15. The method of claim 13, whereinselecting a group of N+M antennas to cooperate in a MIMO transmissioncomprises dynamically defining the group of N+M antennas.
 16. The methodof claim 13, wherein: the wireless nodes comprise at least one mobilestation; and selecting a group of N+M antennas to cooperate in a MIMOtransmission comprises dynamically defining the group of N+M antennas toaccommodate movement of the at least one mobile station.
 17. The methodof claim 13, comprising adaptively selecting between cooperative MIMOand cooperative diversity.
 18. The method of claim 17, whereinadaptively selecting between cooperative MIMO and cooperative diversitycomprises adaptively selecting between cooperative MIMO using a set ofnodes and cooperative diversity using the same set of nodes.
 19. Themethod of claim 17, wherein adaptively selecting between cooperativeMIMO and cooperative diversity comprises adaptively selecting betweencooperative MIMO using a set of nodes and cooperative diversity using adifferent set of nodes.
 20. The method of claim 17, wherein adaptivelyselecting between cooperative MIMO and cooperative diversity comprises:for at least one of cooperative MIMO and cooperative diversitydetermining at least one metric; and selecting between cooperative MIMOand cooperative diversity based at least on the at least one metric. 21.A Multiple Input Multiple Output (MIMO) processing method, comprising:using Space Time Block Coding (STBC), transmitting content for K STBCgroups on K respective groups of antennas, each group of antennascomprising N antennas, K and N each being at least 2; transmittingcontent on M additional antennas, M being at least 1; performing spatialmultiplexing on signals received on at least K×N+M antennas to extractcomponents relating to the content transmitted by the K×N antennas andcomponents relating to the content transmitted by the M antennas;performing a respective STBC processing on the components relating tothe content transmitted by each of the K groups of N antennas to recoverthe content transmitted using the K STBC groups.
 22. The method of claim21, comprising adaptively adding and removing antennas from the K×N+Mantennas.
 23. The method of claim 22, comprising adaptively adding andremoving antennas from the K×N+M antennas due to movement of mobilenodes.
 24. The method of claim 22, comprising adaptively adding andremoving antennas from the K×N+M antennas due to movement of mobilenodes into and out of a coverage area.
 25. The method of claim 21,wherein antennas are allocated to STBC groups adaptively.
 26. A MultipleInput Multiple Output (MIMO) processing method, comprising: a firstwireless node transmitting to a second wireless node; a third wirelessnode transmitting to the second wireless node; and the second wirelessnode performing MIMO processing on signals received from the firstwireless node and the third wireless node; wherein the third wirelessnode retransmits content received from the first wireless node.
 27. Themethod of claim 26, wherein the signals received from the first wirelessnode and the third wireless node are cooperative diversitytransmissions.
 28. The method of claim 26, wherein the first wirelessnode is a mobile station.
 29. The method of claim 26, wherein the secondwireless node is a base station.
 30. The method of claim 26, comprisingthe second wireless node adaptively selecting one of a plurality of MIMOmodes by: for at least one MIMO mode determining at least one metric;and selecting between the plurality of MIMO modes based at least on theat least one metric.
 31. A Multiple Input Multiple Output (MIMO) systemcomprising first, second, third and fourth wireless nodes: the firstwireless node being configured to transmit to a second wireless node;the third wireless node being configured to transmit to the secondwireless node; the second wireless node being configured to perform MIMOprocessing on signals received from the first wireless node and thethird wireless node; and the third wireless node being configured toretransmit content received from the fourth wireless node.
 32. Thesystem of claim 31, wherein the first wireless node is a mobile station.33. The system of claim 31, wherein the second wireless node is a basestation.
 34. The system of claim 31, wherein the second wireless node isconfigured to adaptively select one of a plurality of MIMO modes by: forat least one MIMO mode determining at least one metric; and selectingbetween the plurality of MIMO modes based at least on the at least onemetric.
 35. The system of claim 34, wherein the at least one metriccomprises at least one of MIMO processing gains and diversity gains. 36.The system of claim 34, wherein the MIMO modes comprise at least one ofSpace Time Block Coding (STBC), Spatial Multiplexing (SM) andcooperative diversity.
 37. A Multiple Input Multiple Output (MIMO)system comprising first, second, third, fourth and fifth wireless nodes:the first wireless node being configured to transmit to a secondwireless node; the third wireless node being configured to transmit tothe second wireless node; and the second wireless node being configuredto perform MIMO processing on signals received from the first wirelessnode and the third wireless node; and the first and third wireless nodesbeing configured to receive signals from fourth and fifth wireless nodesrespectively.
 38. The system of claim 37, wherein: the first wirelessnode is configured to transmit content received from the fourth wirelessnode to the third wireless node; and the third wireless node isconfigured to transmit content received from the fifth wireless node tothe first wireless node.
 39. The system of claim 38, wherein: the firstwireless node is configured to transmit to the second wireless node bytransmitting a signal based on both the content received from the thirdwireless node and the content received from the fourth wireless node;and the third wireless node is configured to transmit to the secondwireless node by transmitting a signal based on both the contentreceived from the first wireless node and the content received from thefifth wireless node.
 40. The system of claim 37, configured tosynchronize transmissions from the first wireless node to the secondwireless node with transmissions from the third wireless node to thesecond wireless node.
 41. The system of claim 40, configured tosynchronize transmissions from the first wireless node to the secondwireless node with transmissions from the third wireless node to thesecond wireless node by scheduling transmissions from the first wirelessnode to the second wireless node and scheduling transmissions from thethird wireless node to the second wireless node.
 42. The system of claim41, wherein the scheduling is performed by the second wireless node. 43.A Multiple Input Multiple Output (MIMO) system, comprising: means forselecting a group of N+M antennas to cooperate in a MIMO transmission, Nbeing at least 2 and M being at least 1; means for using Space TimeBlock Coding (STBC), transmitting content on the N antennas; means fortransmitting content on the M antennas; means for performing spatialmultiplexing on signals received on at least N+M antennas to extractcomponents relating to the content transmitted by the N antennas andcomponents relating to the content transmitted by the M antennas; andmeans for performing STBC processing on the components relating to thecontent transmitted by the N antennas to recover the content transmittedby the M antennas.
 44. The system of claim 43, wherein the means forselecting a group of N+M antennas to cooperate in a MIMO transmissioncomprises means for statically defining the group of N+M antennas. 45.The system of claim 43, wherein the means for selecting a group of N+Mantennas to cooperate in a MIMO transmission comprises means fordynamically defining the group of N+M antennas.
 46. The system of claim43, wherein: the wireless nodes comprise at least one mobile station;and the means for selecting a group of N+M antennas to cooperate in aMIMO transmission comprises means for dynamically defining the group ofN+M antennas to accommodate movement of the at least one mobile station.47. The system of claim 43, comprising means for adaptively selectingbetween cooperative MIMO and cooperative diversity.
 48. The system ofclaim 47, wherein the means for adaptively selecting between cooperativeMIMO and cooperative diversity comprise means for adaptively selectingbetween cooperative MIMO using a set of nodes and cooperative diversityusing the same set of nodes.
 49. The system of claim 47, wherein themeans for adaptively selecting between cooperative MIMO and cooperativediversity comprise means for adaptively selecting between cooperativeMIMO using a set of nodes and cooperative diversity using a differentset of nodes.
 50. The system of claim 47, wherein the means foradaptively selecting between cooperative MIMO and cooperative diversitycomprises: means for determining at least one metric for at least one ofcooperative MIMO and cooperative diversity; and means for selectingbetween cooperative MIMO and cooperative diversity based at least on theat least one metric.
 51. A Multiple Input Multiple Output (MIMO)processing system, comprising: means using Space Time Block Coding(STBC) for transmitting content for K STBC groups on K respective groupsof antennas, each group of antennas comprising N antennas, K and N eachbeing at least 2; means for transmitting content on M additionalantennas, M being at least 1; means for performing spatial multiplexingon signals received on at least K×N+M antennas to extract componentsrelating to the content transmitted by the K×N antennas and componentsrelating to the content transmitted by the M antennas; and means forperforming a respective STBC processing on the components relating tothe content transmitted by each of the K groups of N antennas to recoverthe content transmitted using the K STBC groups.
 52. The system of claim51, comprising means for adaptively adding and removing antennas fromthe K×N+M antennas.
 53. The system of claim 52, comprising means foradaptively adding and removing antennas from the K×N+M antennas inresponse to movement of mobile nodes.
 54. The system of claim 52,comprising means for adaptively adding and removing antennas from theK×N+M antennas in response to to movement of mobile nodes into and outof a coverage area.
 55. The system of claim 51, wherein antennas areallocated to STBC groups adaptively.
 56. A Multiple Input MultipleOutput (MIMO) processing system, comprising first, second and thirdwireless nodes: the first wireless node being configured to transmit toa second wireless node; the third wireless node being configured totransmit to the second wireless node; the second wireless node beingconfigured to perform MIMO processing on signals received from the firstwireless node and the third wireless node; and the third wireless nodebeing configured to retransmits content received from the first wirelessnode.
 57. The system of claim 56, wherein the signals received from thefirst wireless node and the third wireless node are cooperativediversity transmissions.
 58. The system of claim 56, wherein the firstwireless node is a mobile station.
 59. The system of claim 56, whereinthe second wireless node is a base station.
 60. The system of claim 56,wherein the second wireless node is configured to adaptively select oneof a plurality of MIMO modes by: for at least one MIMO mode determiningat least one metric; and selecting between the plurality of MIMO modesbased at least on the at least one metric.